Watch as Wolves Magically Transform Yellowstone Park

A captivating look at the role predators play in sustaining a diverse ecosystem.

In an exquisitely produced video posted on the SustainableMan website, investigative environmental journalist George Monbiot explains in just four and a half minutes how the reintroduction of wolves to Yellowstone National Park in 1995 created a so-called “trophic cascade” of positive effects which rippled through ecosystems and even the park’s geography.

Monbiot defines a trophic cascade as an ecological process that starts at top of a food chain and “tumbles down” to its lower levels. “Wolves,” he says, “kill and also give life.” After an absence of wolves from the park for 70 years, huge deer populations had grown up, eating wide swathes of vegetation in different niches of the park.

As the introduced wolves began to feed on deer, not only did they lower population sizes, but they also changed deer behavior. The herbivores began to avoid valleys and gorges where they were more exposed to predators and these areas, in turn, regenerated. In some cases, heights of trees quintupled in just six years. Aspen and willow and cottonwood returned to the valley sides.

With the rebirth of the forests came the arrival of songbirds and migratory birds. Beavers returned to the rivers and created habitats for otters, amphibians, muskrats, ducks, fish, and reptiles. Wolves also killed coyotes and, consequently, the numbers of rabbits and mice began to rise. More hawks, weasels, foxes and badgers, which feed on these small rodents, began to appear in turn. Ravens and bald eagles also appeared to feed on the wolves’ carrion, as did bears. Bears also flourished because more berries were available and, by killing deer calves, the bears reinforced the influence of the wolves.

Amazingly, the small numbers of introduced wolves transformed not only the ecosystem of the national park, but also its physical geography. Regenerated forests stabilized river banks and contributed to transformational changes in the rivers. Banks tended to collapse less often and rivers became more fixed in their courses, meandering less. With less soil erosion due to the presence of regenerated vegetation, more pools formed, channels narrowed, and more riffle sections opened up spaces for ever more wildlife habitats.